The present invention relates to a film-feeding speed controlling device to be applied to a sound-cinecamera.
A typical one of the conventional devices of this kind is as exemplified in FIGS. 1 and 2 of the appended drawings, and therefore hereunder will be given explanation of conventional devices by reference to this example.
As shown FIGS. 1 and 2, this sound-cinecamera is provided with a motor 21 for intermittently feeding the film 25 for the purpose of shooting motion pictures, a capstan driving motor 20 for feeding the film at uniform velocity to record sounds, a detecting switch 22 for detecting any superfluity or insufficiency of the feed of film by said motor 21 relative to the feed of film by said motor 20 and generating corresponding sagsignals, a speed-controlling circuit (a) connected to said motor 21 and comprising a tachometer generator 15 for maintaining the stability of the speed of the motor 21, a delay circuit (c) provided in said speed-controlling circuit (a) and connected to the output side of said tachometer generator 15, and a sagdetecting circuit (b) comprising said detecting switch 22. In this device, the motor 20 is supposed to work steadily at a constant speed, and the motor 21 is supposed to work selectively ether at a high speed or at a low speed as preset, and the detecting switch 22 is in soft contact with the film 25 as shown in FIG. 2.
In FIGS. 1 and 2, the reference numerals 1 and 2 denote the terminals of a power source, 3 through 8 denote resistors, 9 and 10 denote variable resistances, 11 through 14 denote diodes, 16 denotes a smoothing condenser, 17 through 19 denote transistors ,23 denotes a change-over switch, 24 denotes a power supply switch, 26 denotes a pinch roller, 27 denotes a capstan, and 28 denotes a driving mechanism employing the motor 21.
At the time of operating the foregoing device, the motor 21 actuates the driving mechanism 28 which works on the aperture portion of the film for the purpose of image-shooting thereby to feed the film 25 intermittently, and the motor 20 actuates the sound-recording film driving mechanism 26, 27 which works on the film at a position preceding said driving mechanism 28 by a fixed number of frames thereby to feed the film 25 continueously. -
On this occasion, in the case where the motor 21 is running at a high speed, for instance, and the film 25 is excessively fed to cause a sag of film, the detecting switch 22 is turned off and variable resistance 10 is connected, whereby the voltage of the motor 21 is reduced and its rotation is switched over a low speed.
When there occur fluctuations in voltage of the power source for the motor 21 or fluctuations in the load at the time of operation, the output of the tachometer generator 15 in the controlling circuit (a) constituting a servo-system fluctuates and the thus fluctuated output is rectified by the diode 12 and controlls voltage to be applied to the motor 21 via the transistors 17, 18 and 19 through the delay circuit (c) consisting of the resistor 5 and the condenser 16, whereby the speed of the motor 21 can be stably maintained.
In order to maintain the speed of the motor 21 stably as above, it is necessary to reduce the inertia of revolution of the motor 21 as far as possible and to secure the gain for the controlling circuit (a).
For this purpose, it will do to enlarge the difference between the high speed and low speed of the motor 21 and set the feed of film 25 to be, for instance, 10 (feet per second) at the time of the low speed and 26 F/S at the time of the high speed, while actuating the detecting switch 22 for synchronization at 18 F/S.
However, in the case where the difference between the high speed and low speed of the motor 21 is enlarged as above, a damping force arising from actuation of the detecting switch 22 works on the motor 21 so abruptly that the speed of film 25 fluctuates abruptly and/or irregularly and the time for exposure on the occasion of shooting fluctuates, entailing occurrence of undesirable phenomena such as the flickering of image at the time of projection.
Inasmuch as the conventional sound-cinecameras are of such a construction as exemplified above, they have been defective in that an attempt to maintain the controlling efficiency of the servo-system thereof would render it impossible to prevent the occurrence of the flickering of image while an attempt to prevent the occurrence of the flickering of image would render it difficult to maintain the controlling efficiency of said servo-system.